Medical devices

ABSTRACT

An embryo transfer catheter or other medical device has a shaft extruded with two layers. The outer layer is relatively thick and contains gas bubbles sufficient to increase the visibility of the catheter under ultrasound observation but with a density that allows material within the catheter to be viewed by the eye. The inner layer is relatively thin and is free of bubbles so that it provides a smooth bore to the catheter.

BACKGROUND OF THE INVENTION

This invention relates to medical devices.

The invention is more particularly concerned with catheters or the like,that are visible under ultrasound observation.

Ultrasound imaging equipment is increasingly being used during surgicalprocedures to monitor the location of a device within the body. Thevisibility of a device under ultrasound depends on various factorsincluding the difference between the acoustic impedance of the materialof the device and that of the surrounding medium, such as the patienttissue or body fluid w thin which the device is located. This differenceis relatively low with plastic devices such as catheters and may makeconventional catheters difficult to locate. Even devices of metal, suchas needles, present problems of visibility under ultrasound observationbecause of the directional nature of the reflections. In someorientations a metal needle may be clearly visible but in otherorientations it may be considerably less visible.

Attempts have been made to increase the visibility of medico-surgicaldevices under ultrasound observation in various ways. The surface of thedevice may be modified, such as by forming grooves or indentations inits surface. A reflective coating may be applied to the device, such asincorporating bubbles, as described in WO98/19713 and EP0624342.Alternatively, a metal marker may be secured to a plastics catheter.GB2379610 describes a catheter where the wall is made entirely of aplastics including gas bubbles or where bubble-containing material is ina stripe occupying only a part of the circumference. Although thislatter form of catheter has various advantages, it has been found thatthere is a tendency for the surface of the bore through the catheter tobe interrupted by small protrusions where the bubbles break the surface.In some applications, such as for embryo transfer, It is important thatthe bore of the catheter is as smooth as possible so any interruption ofthis is a disadvantage. In other applications it may be importantinstead for the outer surface to be as smooth as possible, or for boththe outer and inner surface to be smooth.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an alternativemedical device.

According the present invention there is provided a medical devicehaving an elongate portion of plastics material, the portion beingextruded with at least a first, inner layer and a second layer on theoutside of the inner layer one of the layers being substantially free ofgas bubbles and the other of the layers including gas bubbles dispersedwithin it to increase the visibility of the device under ultrasoundimaging.

The layer substantially free of gas bubbles may be thinner than theother layer. The layer substantially free of gas bubbles may be theinner layer. The second layer may provide an outer surface of thecatheter. The device may include a third layer on the outside of thesecond layer. The second layer may contain gas bubbles and the first andthird layers may be substantially free of gas bubbles. The bubbles maybe in a region extending around the entire circumference of the device.The bubbles preferably extend in a continuous region along the length ofthe device. The gas bubbles may have a size in the range 0.1μ to 300μ,preferably having a size in the range 1μ to 50μ and roost preferablyhaving a size in the range 5μ to 10μ. The gas bubbles may be provided bygas-filled polymer microspheres. The device may be a catheter having abore extending along its length. The inner layer may have an innersurface providing the bore of the catheter. The plastics material ispreferably transparent to the eye, the density of bubbles being such asto permit material within the catheter to be viewed by the eye.

An embryo-transfer catheter and its method of manufacture, according tothe present invention, will now be described, by way of example, withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a side elevation view of the catheter;

FIG. 2 is a sectional side elevation view of the catheter of FIG. 1 to alarger scale;

FIG. 3 is a cross-section view of the catheter along the line III-III ofFIG. 2;

FIG. 4 illustrates schematically manufacture of the catheter;

FIG. 5 is a sectional side elevation view of a part of an alternativecatheter; and

FIG. 6 is a cross-section view of the catheter of FIG. 5 along the lineVI-VI.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference first to FIGS. 1 to 3, the catheter comprises artelongate portion in the form of a flexible shaft 1 and a hub 2 joined atthe rear end of the shaft. The shaft 1 has a circular section and a bore10 extending along its length. The shaft 1 opens at its forward,right-hand, patient end 11, which is atraumatically rounded.

The shaft 1 is extruded in two layers 12 and 13. The first, inner layer12 is of a clear, transparent polyurethane material and is free of gasbubbles so that its inner surface 14, providing the surface of the bore10, is completely smooth. The second layer 13 is formed around theentire circumference of the first layer 12 and its outer surface 15provides the outer surface of the catheter. The second layer 13incorporates small, gas-filled bubbles 22 the size and distribution ofwhich are selected to increase the visibility of the catheter underultrasound observation. Typically, the gas bubbles have a diameter inthe range of about 0.1μ to 300μ, preferably being between 1μ and 50μwith the most preferred range being about 5μ to 10μ. The bubbles 22extend uniformly through the thickness and around the circumference ofthe second layer 13 and may be spherical or of any other regular orirregular shape. The second layer 13 is preferably made from the sameplastics material as the first layer and the gas bubbles are preferablyprovided by incorporating gas-filled polymer microspheres such as of thekind sold under the trade mark Expancel (“Expancel” is a registeredtrade mark of Akzo Nobel). The bubble-filled layer 13 is preferably asthick as possible so as to increase the visibility of the catheter underultrasound observation. The inner layer 12 may be relatively in sinceits purpose is solely to provide a smooth inner surface for thecatheter.

The hub 2 serves to make connection with the shaft 1 and is moulded froma rigid, transparent plastics material, being subsequently bonded withthe rear end of the shaft.

-   -   The shaft 1 is extruded in the manner shown in FIG. 4 using an        extrusion machine 20. The machine 20 has two extrusion heads 21        and 19, winch are supplied respectively with a polyurethane        material 23 and with a polyurethane material 24 containing        hollow microspheres. The two materials 23 and 24 are heated and        supplied to the respective extrusion heads 21 and 19 so that        tubing is formed with the bubble-filled material 24 coextruded        as the outer layer 13 about the outside of the inner layer 12,        which is of the bubble-free material 23. The shaft 1 can be        extruded continuously at low cost, without the need for any        subsequent operations apart from attaching the hub 2 and end        forming the patient end tip 11.

The bubbles could be formed in various other ways, such as by injectinggas into the melt. Alternatively, chemical foaming agents could be addedto the plastics material, such as: azocarbonomides,dinitrosopentmethelyene-tetramine, benzenephonohydrazine, 4,4oxybis(benzenephonohydrazine), NN¹dimethyl-NN¹ dinitrosoterephthalamide,azoisobutyronitrile, sodium bicarbonate, terephthalazide ortrihydrazinatrazine. Another way of forming the gas bubbles would be byincorporating a liquid into the plastics melt which volatises during themelt process. Alternatively, solid powdered dry ice (carbon dioxide)could be incorporated into the melt so that the particles of dry icebecome gas bubbles during the forming process. It might be possible touse other solids which undergo sublimation in this way. The bubblescould be formed directly as a result of chemical reaction duringpolymerisation and or alternatively during cross-linking. The bubblescould be formed mechanically by whipping the plastics in a liquid form,such as in the manner used to form latex foam. Alternatively, smallparticles of a soluble material could be added to the plastics melt andsubsequently dissolved away.

-   -   The bubble-filled layer need not provide the outer surface of        the catheter, especially where the outer surface of the catheter        needs to be smoother than can be provided by a bubble layer with        bubbles 122. Instead, as shown in FIGS. 5 and 6, the        bubble-filled layer 113 could be sandwiched between an inner        layer 112 and a third, outer layer 116, the inner and outer        layers being of the same material and being free of bubbles.        Preferably, the inner layer 112 and the outer layer 116 are        relatively thin and the middle, bubble-filled layer 113 is        relatively thick, to maximise the ultrasound reflecting        properties of the catheter. This three-layer tube is also made        by co-extruding the three layers with one another.        Alternatively, where it was necessary for the outer surface of        the catheter to be smooth and there was no need for the bore to        be smooth, the catheter could just have two layers where the        outer layer was thin and bubble-free and the inner layer was        thicker and contained bubbles.

The catheter could have any number of additional layers with one or morelayers containing bubbles.

Catheters according to the present invention can be made having goodvisibility under ultrasound imaging without producing multiple echoes.They can produce a good image regardless of the orientation of thecatheter shaft. The shaft can be made sufficiently transparent toultrasound energy to enable material flowing along the bore of thecatheter to be observed on the ultrasound image.

Because the catheter does not require any coating or separate markerthere is no need for subsequent assembly operations and there is no riskof detachment. The catheter can be made of conventional,medically-approved materials so does not present any new risk to thepatient. The outer surface of the three-layer catheter can be smooth sothe catheter can be inserted or slid through an outer tube with lowfriction. A smooth bore can be provided to a catheter to ensure freeflow along the bore, which can be important where the catheter is usedto transfer embryos. In other applications, a smooth inner surface mayreduce the accumulation of biofilm in the catheter. The catheter can bemade without the need for metal components, which can be an advantagewhere the catheter is used while the patient is being viewed by magneticimaging techniques. The catheter can be completely transparent to x-raysor the plastics from which it is formed could incorporate an x-rayopaque filler, such as barium sulphate.

The bubble size and density can be selected so that the opticaltransparency of the plastics forming the shaft remains sufficient toenable material flowing along the shaft to be viewed by the eye.

It is not essential for the bubbles to be provided around the entirecircumference of the bubble-containing layer, instead, the bubbles couldjust be provided along a longitudinal stripe in the layer. Thisarrangement can be used where the shaft needs to have increased clarityso that material within the catheter can be seen by the eye.Alternatively, the bubbles could be contained around the entirecircumference of the layer apart from a bubble-free longitudinal strip.The bubble region need not be continuous along the length of thecatheter. Instead, discrete separate regions with bubbles could beseparated from one another along the length of the catheter by regionswithout bubbles. A shaft for such a catheter could be made by blowinggas into the plastics forming the bubble layer and by interrupting thegas flow. Where the bubbles are contained within a stripe, this could beinterrupted to make it discontinuous by extruding the stripe using twoauxiliary extruders, one having material with hollow microspheres andthe other having material without the microspheres. Alternate extruderswould be switched on and off so that the stripe could have sectionscontaining bubbles separated from one another by sections withoutbubbles. A catheter having a layer with an interrupted bubble region maygive a clearer ultrasound indication of movement of the catheter alongits length and may also enable clearer observation of material flowingalong the catheter both by ultrasound and by the eye.

The invention is not confined to catheters but could be used in othermedical devices such as cables and medical devices without a bore, orwith more than one bore.

What we claim is:
 1. A surgical procedure comprising: placing a medicaldevice within a patient, the medical device having an elongate portionof a first layer of a first polymeric material and a second layer of asecond polymeric material formed around the first layer, the first andsecond layers being coextruded from the first and second polymericmaterials, respectively, the second polymeric material being the same asthe first polymeric material, the first layer being extruded to besubstantially free of gas bubbles and forming an innermost layer of theelongate portion of the medical device, and the second layer beingextruded to include gas bubbles dispersed in its polymeric material andforming an outermost layer of the elongate portion of the medicaldevice, and the first layer that is substantially free of gas bubblesbeing thinner than the second layer that includes the gas bubbles suchthat the second layer forms a main substrate of the elongate portion ofthe medical device; and using ultrasound imaging equipment to monitor alocation of the medical device within the patient, the location of themedical device within the patient being readily observable by theultrasound equipment due to the second layer of the medical device thatincludes gas bubbles providing increased visibility of the medicaldevice under ultrasound imaging.
 2. The procedure of claim 1, whereinthe elongate portion is a catheter having a bore defined by an innerwall of the first layer.
 3. The procedure of claim 2, wherein theelongate portion is an embryo transfer catheter, and the first andsecond polymeric materials are sufficiently transparent to ultrasoundenergy to enable an embryo moving within a lumen of the catheter to bemonitored by the ultrasound imaging equipment.
 4. A method ofmanufacturing a medical device usable for ultrasound imaging, the methodcomprising the steps of: supplying a first polymeric material to anextrusion machine; supplying a second polymeric material to theextrusion machine, the second polymeric material being the same as thefirst polymeric material; coextruding the first and second polymericmaterials with one another to form an elongate tubing with a first layerof the first polymeric material forming an inner wall of the tubing todefine a bore of the tubing and a second layer of the second polymericmaterial formed around the first layer to form an outermost surface ofthe tubing of the medical device; wherein the first layer of polymericmaterial is substantially free of gas bubbles and the second layer ofpolymeric material includes gas bubbles dispersed within its polymericmaterial to increase the visibility of the medical device underultrasound imaging; and wherein the first layer that is substantiallyfree of gas bubbles is thinner than the second layer that includes thegas bubbles such that the second layer forms a main substrate of theelongate tubing of the medical device.
 5. The method of claim 4, furthercomprising the step of: providing gas-filled polymer microspheres to thesecond polymeric material to form the gas bubbles, wherein the gasbubbles have a size in the range 0.1μ to 300μ.
 6. The method of claim 4,wherein the coextruding step comprises extruding the second layer of thetubing to be thicker than the first layer.
 7. The method of claim 4,wherein the medical device is a catheter and the elongate tubing of thecatheter has first and second ends, the method further comprising thesteps of: adding a hub to one of the first and second ends of thecatheter; and rounding the other of the first and second ends to preventtrauma to the patient when the catheter is inserted into the patient. 8.A method of monitoring the location of a medical device within apatient, comprising: placing within the patient a medical device havingan elongate portion with a first layer of a first polymeric material anda second layer of a second polymeric material coextruded with oneanother so that second layer is formed around the first layer, thesecond polymeric material being the same as the first polymericmaterial, the first layer being substantially free of gas bubbles andforming an innermost layer of the elongate portion of the medicaldevice, and the second layer including gas bubbles dispersed in itspolymeric material to increase the visibility of the elongate portionunder ultrasound imaging and forming an outermost layer of the elongateportion of the medical device, and the first layer that is substantiallyfree of gas bubbles being thinner than the second layer that includesthe gas bubbles such that the second layer forms a main substrate of theelongate portion of the medical device; and using ultrasound imagingequipment to monitor the location of the medical device within thepatient.
 9. A method of manufacturing an embryo transfer catheteradapted to be viewed under ultrasound imaging, the method comprising:supplying a first polymeric material to an extrusion machine; supplyinga second polymeric material to the extrusion machine, the secondpolymeric material being the same as the first polymeric material;coextruding the first and second polymeric materials with one another toform an elongate tubing of the embryo transfer catheter, the elongatetubing consisting of a first layer of the first polymeric materialforming an inner wall of the tubing to define a bore of the tubing and asecond layer of the second polymeric material formed around the firstlayer and forming an outermost surface of the tubing of the embryotransfer catheter; wherein the first layer is extruded to besubstantially free of gas bubbles and the second layer is extruded toinclude gas bubbles dispersed in its polymeric material, wherein thefirst layer that is substantially free of gas bubbles is thinner thanthe second layer that includes the gas bubbles such that the secondlayer forms a main substrate of the embryo transfer catheter, andwherein the visibility of the embryo transfer catheter under ultrasoundimaging is increased due to the gas bubbles dispersed in the polymericmaterial of the second layer.
 10. The method of claim 9, furthercomprising the step of: selecting a size and density of the gas bubblesso that the optical transparency of the polymeric materials issufficiently transparent to enable an embryo moving within the bore ofthe elongate tubing to be viewed by eye.
 11. The method of claim 10,further comprising the step of: selecting the size of the gas bubbles tobe in the range of 0.1μ to 300μ.
 12. The method of claim 9, furthercomprising the step of: selecting the size of the bubbles to be in therange of 1μ to 50μ.
 13. The method of claim 9, wherein the coextrudingstep further comprises: coextruding the first layer that issubstantially free of gas bubbles to form a smooth surface for the innerwall that defines the bore of the elongate tubing to reduce trauma toembryos moving through the elongate tubing.
 14. A method ofmanufacturing a medical device viewable under ultrasound imaging, themethod comprising the steps of: supplying a first polymeric material toan extrusion machine for extrusion as a first layer substantially freeof gas bubbles; supplying a second polymeric material to the extrusionmachine for extrusion as a second layer including gas bubbles, thesecond polymeric material being the same as the first polymericmaterial; coextruding the first and second polymeric materials with oneanother to form an elongate tubing consisting of the first and secondlayers, the first layer forming an inner wall of the elongate tubing todefine a bore of the elongate tubing and the second layer formed aroundthe first layer and forming an outermost surface of the elongate tubingof the medical device, wherein the first layer that is substantiallyfree of gas bubbles is thinner than the second layer that includes thegas bubbles such that the second layer forms a main substrate of theelongate tubing of the medical device; wherein visibility of the medicaldevice under ultrasound imaging is increased due to the medical devicehaving the second layer that includes gas bubbles, and wherein the firstand second polymeric materials are sufficiently transparent toultrasound energy to enable material moving within the bore of theelongate tubing to be visualized under ultrasound imaging.
 15. Themethod of claim 14, further comprising the step of: selecting a size ofthe bubbles to be in the range 0.1μ to 300μ.
 16. The method of claim 14,further comprising the step of: selecting a size of the bubbles to be inthe range of 1μ to 50μ.
 17. The method of claim 14, further comprisingthe step of: selecting a size of the bubbles to be in the range of 5μ to10μ.